One of my favorite authors Brandon Sanderson has a rule regarding world building its "Expand what you already have before you add something new."
I think this rule applies with 0 A.D. as well. I don't think it's very fair to our devs to expect research, design, new civilizations, even cool ones when the current civs are still not finished. Even if the civs are perfectly balanced and WFG didn't want to make any other changes, I don't think it'd be fair for them to not have some at least one campaign highlighting a historical event they participated in. (Or cool additional in game information...)
Also, there's more to a game than just adding civs-- and I don't think we should put any expectations on people. Everyone is volunteers, if people want to make and mantain a new civ that's good for them-- but the WFG team needs to feel free to make whatever they want.
I agree-- 0 A.D. at least from my point of view is supposed to have civs firmly grounded in history. We shouldn't change that now. Beowulf would be cool though, but only if I can train Grendles too.
Just as a side note-- with working on the encyclopedia, I have an idea on how hard it is to find information to something, even though I knew exactly what I'm looking for. Writing for the Han dynasty was hard-- and when I tried to find things on the Kush it was difficult too. I can only imagine how hard it would to get information for civilizations without widely available primary sources, even as a research project that would give me nightmares-- even more if I don't have money to purchase archeological journals.